linux-kernel - Re: [RFC PATCH 5/7] x86/mm/fault: hook up SCI verification

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Date:   Sun, 28 Apr 2019 08:47:11 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Jonathan Adams <jwadams@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Paul Turner <pjt@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, linux-mm@...ck.org,
        linux-security-module@...r.kernel.org, x86@...nel.org
Subject: Re: [RFC PATCH 5/7] x86/mm/fault: hook up SCI verification

On Fri, Apr 26, 2019 at 09:42:23AM +0200, Peter Zijlstra wrote:
> On Fri, Apr 26, 2019 at 12:45:52AM +0300, Mike Rapoport wrote:
> > If a system call runs in isolated context, it's accesses to kernel code and
> > data will be verified by SCI susbsytem.
> > 
> > Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> > ---
> >  arch/x86/mm/fault.c | 28 ++++++++++++++++++++++++++++
> >  1 file changed, 28 insertions(+)
> 
> There's a distinct lack of touching do_double_fault(). It appears to me
> that you'll instantly trigger #DF when you #PF, because the #PF handler
> itself will not be able to run.

The #PF handler is able to run. On interrupt/error entry the cr3 is
switched to the full kernel page tables, pretty much like PTI does for
user <-> kernel transitions. It's in the patch 3.
 
> And then obviously you have to be very careful to make sure #DF can,
> _at_all_times_ run, otherwise you'll tripple-fault and we all know what
> that does.
> 

-- 
Sincerely yours,
Mike.